Blood cells are produced by a process known as hematopoiesis. The source of all blood cells is the hematopoietic stem cell (HSC). As the stem cell gives rise to cells which become committed blood cells, they must be renewed or duplicated. Hematopoiesis is regulated by a group of factors known as hematopoietic growth factors. There are factors which affect cells early in development, midway through development, and late in development. These factors act through cell surface receptors to regulate the growth and development of these cells. When there is a need for blood cells, these factors are up-regulated. The factors in turn stimulate an increase of production of the specific blood cell type required. With analogy to the regulation of the other hematopoietic cells development, the renewal of stem cells appears to be under the regulation of a growth factor called stem cell renewal factor (SCRF). During Phase I, novel research tools were developed and an important collaboration was established with an academic laboratory. These developments will enable the goal of isolating the cDNA encoding SCRF to be accomplished in Phase II. In addition, production processes and purification scheme will be developed and animal studies will be performed. SCRF will be useful for the treatment of cancer patients to increase production of blood cell, as a pretreatment to collection of peripheral hematopoietic stem cells for autologous stem cell transplantation, and as an agent to amplify stem cells in culture for stem cell transplantation and gene therapy.